Ultrasonic energy has been applied to prior flow separation situations but, insofar as known to Applicants, not to crossflow filtration of liquids in the above mentioned field.
The Assignee of the present invention has developed, over time, filter systems for difficult to filter liquids, such as liquid solutions, suspensions and the like having a high solids content, particularly certain liquids of a viscous nature or otherwise having a high solids content such as colloidal gels, mineral and clay slurries, starch solutions, petroleum oil products and the like, in which the solids tend to coagulate or coalesce, wherein the filtering out of large impurity elements is a difficult problem. Such problem was early recognized in, for example, Petter, et al. U.S. Pat. No. 3,161,159, assigned to the Assignee of the present invention.
Subsequent Davis U.S. Pat. No. 5,198,111; Davis et al. U.S. Pat. No. 5,527,462 and Vander Ark U.S. Pat. No. 5,569,383, all assigned to the Assignee of the present invention, require, (per housing) a single, relatively large diameter, cylindrical filter element which uses barrier filtration flow from inside out. A cleaning member moves along the inlet surface of the filter element to mechanically wipe or scrape solids from the filter element gaps back into suspension in the liquid to be filtered.
Later DeKock et al. U.S. Pat. No. 6,395,186 provides such a wiper/scraper, barrier type, filter unit, in which plural ultrasonic transducers are spaced axially and circumferentially on the outside of the filter housing to assist barrier filtration of composite liquids including particularly aggressively coalescing solids particles, which would otherwise quickly blind the filter element at a commercially unacceptable rate.
The above discussed filter systems use barrier-type filtration processes, wherein all of the incoming process liquid must pass through the filter element to be stripped of unwanted relatively large impurity elements, namely those size of larger than the filter element gaps.
Further, each of the prior filter systems above discussed, has, within a given filter housing, only one or perhaps up to three, filter elements, and hence a relatively low area of filtration material (e.g. screen) per filter housing.
In a continuing effort to improve efficiency in filtering difficult liquids, particularly of the kind above discussed, Applicants have found that in certain situations, all of the process liquid, going to a user process, need not be filtered (e.g. in certain oil refinery processes). Moreover, Applicants have found that there is often very little space available for filtration equipment in a given liquid process installation, so as to make desirable the maximizing of filter media area while minimizing the outside dimensions of the filter housing.
Accordingly, the objects and purposes of the invention include provision of methods and apparatus for filtration, commercially acceptable flow rates and flow durations, using crossflow filtration and ultrasonic energy for preventing bridging of filter element gaps, without need for mechanical wiping/scraping, for difficult to filter process liquids (e.g. of the kind having (1) a carrier liquid, (2) coalescing solids particles which tend to stick together to bridge and thus blind a filter element gap sized larger than the width of such particles, and (3) larger impurity elements to be filtered out of such process liquid and sized larger than such a filter element gap).